1. Field Of The Invention
2. Description of Related Art
Coiled tubing is pipe which can be run in and out of a bore, pipeline, tubular string, borehole, or wellbore. In certain embodiments, the coiled tubing is made of plastic, composites, titanium or steel. The tubing is stored on a reel and in winding onto the reel it is bent. Typically the coiled tubing is fed from the reel over a gooseneck of an injector for directing the tubing into a bore hole. The injection operation often results in further bending of the coiled tubing. Often there is some internal pressure inside the coiled tubing while it is being bent. Also axial loads are applied to the coiled tubing both while it is being bent and while it is straight. Repeated bending cycles can damage the coiled tubing. The internal pressure and axial loads can exacerbate this damage. This damage, known as fatigue damage, accumulates until the coiled tubing eventually fails. Failure is defined as the point at which the coiled tubing can no longer hold internal pressure, or, in extreme situations, the point at which the coiled tubing breaks. After use of the tubing downhole, the tubing is withdrawn from the well and rewound on the reel. The reel has a reel support frame normally mounted on a skid. The skid with the reel and wound tubing thereon may be transported from one site to another. Characteristics of the coiled tubing on which accurate data is required involves fatigue and deformation of the coiled tubing. Coiled tubing is fatigued and/or deformed when it is run in and out of a hole or bore particularly from bending and straightening at the reel and/or gooseneck. Fatigue and deformation are dependent also on other various factors such as axial forces applied to the tubing, the fluid pressure within the tubing while it is being bent or straightened, the tubing material, and the internal and external diameters of the tubing. Parameters have been established for selected features or characteristics of the coiled tubing and its usage. The life expectancy of the tubing may be estimated from such parameters. "Fatigue life" is defined as the useful life of the coiled tubing up to the point of failure due to fatigue. In some coiled tubing operations the length of the fatigue life strongly affects the economics of the operation. The coiled tubing is expensive, and must be replaced at the end of its fatigue life or when it has become too deformed to be used.
In certain prior art systems an operator at each job site is responsible for obtaining and recording pertinent data in a database for the coiled tubing. The updating of the database for each coiled tubing reel may be mandated by certain operators and has generally been performed either manually or by a suitable electronic data acquisition system, for example.
Fatigue factors for coiled tubing include the radii of bending, diameter, wall thickness and length of the coiled tubing. Repeated bending cycles, internal pressure and axial loads can cause the coiled tubing to change in diameter, length and wall thickness. Such changes are permanent deformations that can cause problems when using the coiled tubing.
Fatigue tracking systems have been developed to track the bending events and internal pressure along the length of a coiled tubing string. These systems may also track the axial forces applied to the coiled tubing both while bending and while straight. These systems then use mathematical models to predict the fatigue damage and amount of the fatigue life used. Some of these systems also predict the permanent deformation which will occur along the length of the coiled tubing string.
Often the coiled tubing rotates during its use. A certain segment of the coiled leaves the reel in one rotational orientation, and returns in a different rotational orientation. If the segment has rotated, the neutral axis of bending has also changed, changing the fatigue damage and deformation when compared to a segment which has not rotated. Prior art fatigue tracking systems do not take this rotation into account when calculating fatigue damage and deformation. Many current fatigue tracking systems were developed based upon the assumption that the coiled tubing does not rotate. In some tests done to develop such systems, the coiled tubing was not rotated. Thus, in such tests, the impact of rotation on fatigue life and deformation was not measured.
Recent testing performed by the present inventor and his associates included rotation and axial loading along with the bending and internal pressure. This testing revealed that in many cases rotation increases the fatigue life. In some cases rotation also increased the amount of deformation.
When the coiled tubing is being used, rotation is random and uncontrolled. This random rotation may increase the fatigue life. With the current systems which do not take rotation into account, coiled tubing may be scrapped earlier than necessary, sometimes at a large cost to the industry. The present inventor has recognized that monitoring rotation and including it in a fatigue tracking system would allow the life of coiled tubing to be extended in some cases. In other cases controlling rotation of coiled tubing could extend its useful life, and hopefully, optimize it.
There has long been a need, recognized by the present inventor, for a method that takes coiled tubing rotation into account in making fatigue life determinations and for systems useful in such a method.
FIG. 1 shows a prior art coiled tubing system which does not measure the rotation of the coiled tubing. The system is disclosed in U.S. Pat. No. 5,826,654 which is incorporated herein fully by reference. The system of FIG. 1 is a system for sensing, recording, and storing data concerning characteristics of coiled tubing so that the data may be easily retrieved at another job site. A coiled tubing reel is shown at 10 mounted on a skid 12 for transport from one job site to another job site. A reel frame 13 on skid 12 mounts reel 10 for rotation. Coiled tubing shown at 14 is wound onto reel 10 and is unreeled for being injected downhole. Coiled tubing 14 is used for many downhole applications. A gooseneck 18 of a wellhead injection device 16 diverts the coiled tubing 14 vertically downwardly. Wellhead injection device (injector) 16 includes a drive mechanism for forcing tubing 14 downwardly. A lower wellhead structure 20 receives tubing 14 and normally includes a blowout preventor (BOP) stack.
A skid 12 with reel frame 13 and reel 10 thereon may be transported from one job site to another job site often thousands of miles apart. A reel database 22 is permanently mounted on frame 13 for coiled tubing 10 prior to its use at the first job site. The reel database 22 is permanently fixed with and travels with reel 10 for the entire life of coiled tubing 10. Database 22 includes a memory unit where information concerning coiled tubing 12 is stored for retrieval at each job site.
A continuous cable loop 26 originates at a Coiled Tubing Sensor Interface (CTSI) 28 which forms a main data processing unit at a job site and is looped about and between the equipment or various elements of the system for termination back at CTSI 28. Wires in the cable provide power and distribute data to and from various Sensor Interface Modules (SIMS) 30A, 30B, 30C, 30D, 30E, 30F and 30G located along the continuous cable loop 26. The Coiled Tubing Sensor Interface (CTSI) 28 permits an automatic update and maintenance of reel database 22. A Sensor Interface Module (SIM) is provided for monitoring each of the selected characteristics or features of the coiled tubing. The SIMs are capable of receiving and/or sending data concerning the selected characteristics or features. A SIM 30A for reel 10 includes database 22. The location and number of the sensor interface modules (SIMS) might vary from one job site to another job site.